Centrifugal fan with wave trap and cut-off



May 17, 1955 w. J. CALDWELL CENTRIFUGAL FAN WITH WAVE TRAP AND CUT- OFF Filed June 27, 1951 INVENTOR BY almmm ATTORNEY atent flice Uni d t Patented May 17, 1955 acteristic. Second, and of considerable importance, is the fact that the compression waves resulting from the 2,703,546 against the perforated cylinder surface are not reflected .3 from this surface, as in the case of a solid surface, but

i fig g ggg TRAP follow the pattern of airflow against a conventional perforated acoustic ceiling, with these sound waves being William J. Caldwell, Independence, Mo. admitted through the cylinder perforations to pass into the cylinder. Here, the presence of the axial slot 20 Apphcanon June 1951 serial 23375l it) has significance. The existence of this slot breaks up 2 Claims. (Cl. 230-114) the presence of a continuous reflecting surface Within the This invention relates to centrifugal fans and in parl5 place.

ticular to centrifugal fans of the character disclosed in These pressure type centrifugal fans exhibit considerable my prior Patent No 2 335,734 issued November 30 1943. sensitivity to the position of the cut-off device if the best According to the centrifugal fan disclosed in my said air delivery performance is to be obtained To provide by the action of the fan blades. In connection ith periphery of the fan blade assembly in a radial direction such a fan assembly, designed to compress air to 3 inches, but also transversely With sp t the discharge 1102' for example, the passage of the fan blades past this cutl ofi' gate has been found to give rise to a buzzing noise Th adj ments are possible by providing oval holes due to the slapping of the air stream against the gate 22 n the pp Walls of the Casing 14, thlollgh which and the sudden arresting of the air flow by the impingeholes spindle-like extensions 24 at the cylinder ends merit of the velocity of air against the cut-off gate. This extend t the outside f the casing Walls an receive buzzing noise is a characteristic of pressure type fans IheFeOVeI', in turn, a Sealing disc 26, a Washer and of these waves being in excess of the velocity of the Cation Ofthe Cylinder 10,88 above Stated p y by loosennormal air flow through the fan assembly, ing the nuts 30 and shifting the cylinder within the It is an ob ect of the invention to provide an improved limits of the holes with r p to Which th discs centrifugal fan assembly in which the above stated dis- 26 Provide an effective Seal in the tightened cohdiiiml advantages of a fixed cut-off are avoided. 0f h nuts 30.

It is another object of the invention to provide a cen- In IV I have shown a modified Construction Of trifugal fan having an improved cut-off which is quiet in Cut-01f Silencer involving three Cylinders 36 operation. 40 ranged in nested radially spaced eccentric relationship,

These, and further objects and advantages of the as Shown, With each Cylinder Presenting a Perforated invention will appear clear from consideration of the face to the a flow m h an and th Siz of th following description with reference to the drawings in perforations varying desreasingly in size from the Outerwhich: most cylinder to the innermost one. Thus, the perfora- Fig. I is an end view of a fan assembly h i a peptions in cylinder 32 may be /3" diameter, in cylinder 34, forated and slotted cylindrical cut-off silencer according /32", and in Cylinder 36, /16" diameter- This triple Y to the invention, inder assembly is mounted within the fan housing outlet Fig. II is a section on the line II II of Fig. I, duct or nozzle 38 in close proximity to the discharge Fig III is an exploded perspective view of the cutside of the fan, shown in outline at 40 and may be sup- 01f cylinder and its ad ustable mounting means, and 70 ported therein upon axially spaced brackets one of which Fig. IV is a cross-section of a fan housing w th a al. is shown at 42, whereas the two inner cylinders 34 and ternative cut-off silencer in accordance with the inven- 6 y be eemplete cylinders, as Shown The Outer tion. cylinder 32 may be constituted by a perforated sheet said prior Patent No 2 335,734 but, referring first to Having thus described my invention what I claim as Figs I to III includes an improved cut-off silencer device new and desire to protect by Letters Patent is in the form of a cylinder 10 mounted in the fan dischar e In a centrlfugal fan having a casing with a disperiphery of the fan blade assembly 16, the rotary shaft to discharge pressure air through said nozzle, a cut off disposed to face downstream with respect to the dissaid fan assembly, Sald elongated member having all P- charge of the pressure air through the nozzle 12, as shown stream perforated surface presented to the pressure air in Fig. II. discharged from said fan assembly, the down-stream sur- This cylindrical cut-off device possesses distinct adface of said member defining an enlarged opening extendvantages over the fixed gate structure of my prior patent. ing longitudinally along the axis of said elongated mem- First, the cylinder 10 presents a blunt impact surface, her and transversely of the stream of pressure air. much like the leading edge of an aerofoil, and permits 2. The invention as defined in claim 1, means adjustthe impinged air stream to seek its best streamline charably mounting said cut-off cylinder in MM means permitting the cylinder to be adiusted radially 1,990,860 Ellsworth Feb. 12, 1935 with respect to the fan assembly and transversely with 2,015,210 Witzel Sept. 24, 1935 respect to said discharge nozzle. 2,107,897 McMahan Feb. 8, 1938 2,160,666 McMahan May 30, 1939 References Cited in the file of this patent 5 1,171,341 M h Aug 29 1939 UNITED STATES A T 2,214,467 Lambert Sept. 10, 1940 2 225 398 Hamblin Dec. 17 1940 1,043,966 Oldberg Nov. 12, 1912 1,840,082 Breer an 5, 1932 2,335,734 Caldwell 1943 

